The phrase “Intrinsically Safe” is often used generically to describe products destined for hazardous (explosive) areas. This paper explores the term “Intrinsically Safe”, provides an overview of what is required to certify a product and compares Intrinsic Safety against Explosion Protection concepts.
Intrinsic Safety – the basics
The term “Intrinsically Safe” (I.S.) is frequently used to describe any product destined for an explosive area. In reality, I.S. is a protection concept based around limiting the available electrical energy to nonincendive levels so that sparks cannot occur from short circuit or failures which could cause an explosive atmosphere to ignite.
A typical fixed I.S. circuit would comprise a device such as a temperature sensor permanently located within the explosive area, which is in turn protected by a safety barrier located in the safe area. These barriers usually incorporate a series of diodes, resistors and fuses arranged and sized in such a manner that they limit the energy provided to the device in the field. Interestingly, the inclusion of a barrier in the control loop does not allow any device to be connected downstream. Even though the power may be limited, the device located within the explosive area itself must also be designed to comply with the requirements of various regulatory standards depending upon the geographical locale of the plant.
Explosion-Proof technology – why use it??
Okay, so I.S. equipment is usually light, compact and robust, everything we need for a portable device. So, why would anyone want to use explosion-proof (XP) as a protection concept?
The answer is simple: power.
With an I.S. system the entire power of the system - which includes but is not limited to the batteries – is controlled. This means that inductive and capacitive loads are also assessed to the extent that they cannot cause a spark.These limitations can cause problems when a device needs to operate in a power range higher than allowed. High Voltage Switchgear for example could never be considered I.S. as the power in the conductors is far higher than that accepted by the I.S. standard. Similarly, high energy components such as a camera flash cannot be part of an I.S. device as the flash itself is powered by a capacitor which has a discharge greater than accepted.By using XP as a protection concept, “high” power devices can be used safely in an explosive area. The XP device itself is designed and tested to contain any explosion which may occur within, protecting the operator and the facility from harm.
Source: http://www.transcat.com/technical-reference/PDFs/Application%20Notes/cordex-is-explosion-proof.pdf
